A number of MEMS-based micro-valves have been reported in the literature using a variety of actuation methods, including: pneumatic; electrostatic; thermo-pneumatic; shape-memory alloy (SMA); thermal bimetallic; piezoelectric; and electromagnetic.
All of these micro-valves previously reported in the literature have been 2-way devices that can merely “open” or “close” to allow the device to “turn on” or “turn off” the flow of fluid through the structure. Importantly, none of these devices can be operated as three-way micro-valves that can direct the flow of fluid in a preferred direction. This is partly due to the fact that MEMS is, in general, a relatively new technology, and specifically because MEMS-based micro-valves are even less mature. Consequently, the only available method for the implementation of a fluidic system wherein the fluid can be directed to a preferred direction has been to use at least a quantity of at least two (2) separate two-way micro-valves. However, this is an expensive solution that doubles the power required, size, weight and space, as well as reduces reliability, and therefore is not an optimal or preferred solution for many applications.
A major challenge for MEMS-based actuators in general, and micro-valves in particular, is the very low actuation forces that can be generated on the small dimensional size scales of the actuator elements. The resulting small actuation forces typically prevent these types of devices to be used where the actuator must overcome larger forces. For example, a typical electrostatically-actuated micro-valve will only generate less than a 1 psi (pound per square inch) of actuation pressure. Therefore, if the micro-valve actuator must overcome the fluid pressure in order to open and/or close the device to the flow of fluid, then the micro-valve would be restricted to applications where the fluid pressures are smaller than the actuation pressure, which is less than 1 psi.
Disclosed herein is a three-way micro-valve device and method of fabrication that can be tailored to the requirements of a wide range of applications. The disclosed 3-way micro-valve can use a number of different actuation methods, including actuation methods that have very small actuation pressures while being able to control fluid pressures much higher than the pressures that can be generated by the actuator. The micro-valve of the present invention employs a pressure balancing scheme so that it can be actuated while controlling fluid pressures much larger than the actuation pressure generated by the actuator.